A new class of unusually potent antitumor drugs modeled after the alkylating antibiotic CC-1065 (isolated from Streptomyces zelensis) are being developed as clinical candidates. Based upon observations of the parent drug a number of novel features have been noted. The drugs bind within the minor groove of DNA in a highly sequence specific manner. A covalent bond is formed with N3 of adenine under proper steric conditions. While the unusually high cytoxicity activity (at <nM concentrations) appears to match a potential to induce adducts on cell free DNA, not much is known about the behavior of these drugs in cells. The goal of this project is to examine the potential of these agents to modify the structure and function of cellular DNA as a means to understand the basis of their cytotoxic activity. Initial emphasis is placed on the parent compound and three clinical candidates (which are likely to possess novel mechanisms of action) that are either in phase I trials or under active consideration for such testing. The following is a summary description of the specific aims: 1. To determine the ability of CC-1065 and its analogs to form DNA lesions (covalent adducts) in cellular DNA. The goal of this work is to assess drug action on its primary cellular target DNA, and to delineate structural factors within the genome that influence drug activity. Drug action on potentially vulnerable subpopulations of DNA will be studied by determining lesion formation with replicating and transcribing regions of the cellular genome. 2. To evaluate the consequences of adduct formation on DNA function. This study will determine how DNA replication and transcription processes are affected by drugs capable of damaging (perhaps preferentially) replicating and transcribing regions. 3. To assess the consequences of adduct formation on cell death. We will evaluate whether covalent adduct formation is causatively linked to the cytotoxic activity of CPI compounds. Correlations will be sought between drug effects on DNA structure and/or function and cell killing. In addition hamster and human cell mutants selected for their resistance to CC-1065 and its analogs will be examined for their susceptibility to DNA damage by these drugs, and to determine relevant mechanisms of resistance.